Processes for producing a two-dimensionally extending metallic microstructure are known in which a molding tool is formed having a surface which comprises numerous microstructures. The two-dimensionally extended microstructure body may, for example, be a foil or plate which is used for filtering liquids or is used as a diffraction grating.
The molding tool which contains a microstructure body is used to form a female mold corresponding to the shape of the microstructure body. The female mold is made from a molding material which comprises a composite body in the form of an electrically-insulating layer and an electroconductive layer. In order to make the female mold, the microstructures of the tool can be pressed through the electrically-insulating layer into the electroconductive layer. The tool containing the microstructure body is then withdrawn from the composite body to form an impression or negative imprint in the composite body. The female mold thus produced can, by using the electroconductive layer as a cathode, be electroplated with a metal to form a metallic microstructure body. The female mold can then be removed from the new microstructure body. The molding tool can then be reused to form a new female mold and the process can be repeated.
Microstructure bodies may be produced by either of two different methods: (1) photolithography combined with electroplating or (2) the process disclosed in German PS 35 37 483. This latter process is called the "LIGA" (deep-Etch x-ray lithography-microelectroforming) process.
It is also apparent from the German Offenlegungsschrift DE-OS 36 11 732 that for producing catalyst-carriers, individual plate-shaped microstructure bodies, produced by the LIGA process, can be aligned and combined into a solid structure.
In the method where photolithography is used in conjunction with electroplating, thin resist layers are generally used because, the structuring of thick photoresists creates problems. The adjustment of the opening sizes is accomplished by freely growing an electroplated layer above the resist structure. The photolithography method is based on the irradiation of a resist layer by UV light. The UV-radiation penetrates the resist layer only to a depth of about 50 .mu.m to 100 .mu.m at best. The predetermined size of the openings can be adjusted as a function of the thickness of the electroplated layer. However, transparency is thereby greatly reduced, particularly as the size of the openings decreases. Therefore, high transparencies, small openings, and thick plates cannot be realized simultaneously. Moreover, the achievable tolerances for these openings are consequently highly dependent on the parameters of the electroplating bath.
The LIGA process in accordance with German PS 35 37 483 cannot produce microstructures in which the cross sectional form changes by means of the height of the microstructure. In other words, the opening dimensions cannot be adjusted through the height of the electroplate layer.
Those working in the art are therefore faced with the problem of avoiding the above-mentioned disadvantages.